Boron fuels



3,667,257 Patented Dec. 4, 1962 3,067,257 BORGN FUELS Timothy Altares, Jr., Evans Qity, Pa, assignor to Gallery Chemical Company, Pittsburgh, Pa, a corporation of Pennsylvania No Drawing. Filed .lune 22, 1959, Ser. No. 822,714 7 Claims. (Ci. 260-6065 This invention relates to boron-containing high energy fuels, and more particularly to liquid boron fuels and a method for improving their properties.

In the high energy fuel art, liquid fuels containing boron have become increasingly important. Due to their high heat of combustion and specific impulse compared to conventional hydrocarbon fuels, liquid boron fuels have been developed which are useful with various engines and propulsion systems in which their properties can be economically utilized.

A number of methods for making boron fuels have been developed and are being used in the production of high energy fuels. Several of these processes are related and depend upon the reaction of boron-hydrides with unsaturated hydrocarbons; the liquid fuels thus produced contain alkylated higher boranes as their main constituent. Several examples of such fuels and processes are described in copending applications of common ownership with this application, such as the application of Eads and Brandt, Serial No. 546,817, filed November 14, 1955, which describes a method of preparing a high energy fuel in which excess diborane and ethylene are reacted at superatmospheric pressure and elevated temperatures. Similarly, the application of Huff and Hunt, Serial No. 546,822, filed November 14, 1955, now abandoned describes a process in which diborane is reacted at elevated pressures with the reaction product of diborane and an unsaturated lower aliphatic hydrocarbon. Other processes in which high energy fuels are prepared from boron hydrides and unsaturated hydrocarbons are described in the applications of Lichtenwalter and Harwell, Serial No. 569,945, filed March 6, 1956, now US. Patent No. 2,979,530; Brault and Huff, Serial No. 745,801, filed June 26, 1958; Judd and Richmond, Serial No. 605,688, filed August 20, 1956; and Kendrick, Eads and Wagner, Serial No. 716,514, filed February 20, 1958.

The processes described in the above mentioned applications are examples of processes which can be used to prepare crude liquid boron fuels. The term crude liquid boron fuel as it is used herein means compositions containing boron, carbon, and hydrogen which comprise substantial amounts of alkylated higher boron hydrides, i.e., alkyl boranes having 4 to 12 boron atoms per molecule, and which are obtained as the products of various processes such as those described above in which boron hydrides and unsaturated hydrocarbons are reacted at varying conditions of temperature and pressure. These processes in general comprise either the reaction of a boron hydride and an unsaturated hydrocarbon to produce a crude liquid boron fuel directly, or a method in which an intermediate product of diborane and an unsaturated hydrocarbon, such as a mixture of alkyldiboranes, is first obtained and then further reacted with a boron hydride.

Although the crude liquid boron fuels vary in their exact composition, they all contain as their main constituent alkylated hi her boron hydrides, such as alkyl decaboranes and alkyl pentaboranes. All these crude liquid boron fuels have a high heat of combustion compared to hydrocarbon fuels and are useful as high energy fuels. However, they have certain undesirable physical characteristics. For example, the crude fuels as they are produced tend to deposit gummy residues in fuel lines and in storage, in many cases their viscosity is higher than is desirable and they often have relatively poor thermal stability.

It is, therefore, an object of this invention to provide new improved liquid boron fuels which are not subject to the foregoing disadvantages and which have improved physical properties.

Another object is to provide a process for improving crude liquid boron fuels which is easier to carry out and which is more effiecient than the process used previously to achieve these ends.

Still other objects will become apparent from the following specification.

In the copending, coassigned application of Severini, Serial No. 716,509, filed February 20, 1958, there is described a process for producing improved liquid boron fuels from crude liquid boron fuels which comprises treatment of the crude liquid boron fuel with a fluid saturated hydrocarbon. In this process, certain solid components of crude liquid boron fuels are precipitated in solid form and are removed by filtration, centrifugation or similar procedures. While that method has provided a major improvement in the boron fuel art, it has been found to be subject to certain disadvantages. For example, the separation step, i.e., filtration, centrifugation or similar method, is relatively timeconsuming, and some solids which are formed in the process are of microscopic size and are therefore almost impossible to remove. Furthermore, and possibly due to these residual solids, the improved liquid boron fuel obtained, although of improved stability, is not as stable as is ultimately desired.

This invention is predicated upon my discovery that treatment of a crude liquid boron fuel with a mixture of a fluid saturated hydrocarbon and an alcohol results in an improved liquid boron fuel. The improved liquid boron fuel thus produced is comparable in all respects, and is superior in stability, to that produced in the former process; in addition, the process and fuel are not subject to the disadvantages mentioned above.

When, in accordance with this invention, an alcohol is used in conjunction with the fluid saturated hydrocarbon, two layers are produced in the crude liquid boron fuel. The solid components are found in the bottom layer as a viscous liquid, while the top layer comprises an improved liquid boron fuel as a solution in the hydrocarbon. Removal of the hydrocarbon is easily accomplished by conventional techniques, e.g., by stripping. I have further found that more complete removal of the undesirable components is attained by the use of my method. Thus, in most cases less than 0.5 weight percent of normally solid components remain in the improved liquid boron fuel, and in many cases none remain, whereas it has been generally found to be impossible to obtain an improved liquid boron fuel containing less than about 3 weight percent of normally solid components from the treatment with a hydrocarbon alone. Other advantages resulting from the use of my method include relatively easy separation, since two liquid layers are produced which can be separated by simple decantation or similar technique, and a more stable improved liquid boron fuel as the product.

Any liquid alcohol may be used in the practice of this invention, including, for example, methanol, ethanol, isopropanol, higher alcohols such as hexanol, and aromatic alcohols such as benzyl alcohol. However, the use of higher and more complex alcohols results in slower reaction and separation of layers and increased difiiculty of removal if the alcohol is present in excess, due to their lower volatility. Furthermore, higher alcohols require their use in larger amounts, so that it is preferred to use the lower alcohols. Methanol is particularly preferred, since not only is it the most volatile alcohol, but less of it by weight is required for complete removal of the solid components. In addition, methanol is miscible with pentane and hexane, the preferred hydrocarbons, so that better contact is achieved Without the need for excessive agitation.

Any fluid saturated hydrocarbon may be used in conjunction with the alcohol. Examples of the hydrocarbons which may be used include butane, pentane, hexane, heptane or cyclohexane. The separation of the layers produced, however, must be carried out while the hydrocarbon is in liquid form, so that if a gaseous hydrocarbon is used, low temperatures or higher pressures are needed. On the other hand, the use of higher hydrocarbons, which are less volatile, presents problems similar to the use of higher alcohols; thus, the preferred hydrocarbons are those which are liquids but which are of high volatility, such as hexane and, in particular, pentane.

The concentration of the alcohol in the mixture is not critical since any amount of alcohol when used with the hydrocarbon results in some degree of separation. It is generally preferred, however, to use at least 2 Weight percent of the alcohol in the hydrocarbon, while over weight percent is not usually required, and may even be less effective.

The use of very high concentrations of alcohol often results in a homogeneous mixture rather than a separation of two liquid layers. The maximum concentration which may be used with good results depends in large part upon the composition of the crude liquid boron fuel being treated, and in particular upon the amount of undesirable solid components contained in the crude liquid boron fuel. Table I below sets forth the approximate maximum concentration of methanol in pentane which I have found to be practically useful in treating crude liquid boron fuels containing various proportions of solid components.

Table I Weight Percent Weight Percent Solids in Crude Methanol in Fuel Pentane While the ratio of the treating mixture to the crude liquid boron fuel does not appear to affect the maximum concentration of alcohol which should be used, the ratio used does in some measure determine the optimum concentration of alcohol. Another factor which is important in fixing an optimum concentration for any system is the particular alcohol being used.

While the use of an excess of the treating mixture is not absolutely necessary, inasmuch as some separation is achieved regardless of the relative amounts of the fuel and the treating mixture, in order to achieve a clear separation of the liquid layers it is preferred to use at least a 10 to 1 volume ratio of treating mixture to fuel. The use of such higher ratios is desirable because it results in faster separation as well as in more complete removal of the solidcomponents. In determining the ratio best suited for use in a particular system, the concentration of the alcohol in the hydrocarbon as well as the particular alcohol must be considered since their effects are interrelated.

I have found, for example, that when a methanol-pentane mixture is used and the concentration of the alcohol is about 2 weight percent, at least about a 20 to 1 volume ratio of the mixture of the fuel should be used. At a 6 weight percent concentration, a 10 to 1 volume ratio is sufiicient to obtain good results, although a 20 to 1 ratio is somewhat better. At 9 weight percent, a 10 to 1 ratio appears to be high enough. However, for the most economical, complete and fastest removal of the solid components, it is at present preferred to use about a 3 to 6 weight percent mixture and a 30 to 1 volume ratio.

The efliciency of the method described herein is increased by providing good contact between the fuel and the treating mixture. Accordingly, agitation during the treatment is recommended in order to provide faster and more complete separation of the solid components. Thus, in tests in which normal agitation was used, of the solid components were removed in three minutes, and complete removal was achieved in about ten minutes; even in one minute about half of the solid components were removed.

In one series of tests, the efficiency of this method in removing solid components, as well as the effect of varying the concentration of the alcohol in the hydrocarbon and of various volume ratios of the treating mixture to the fuel, were determined. In these tests, a mixture of methanol and pentane was used to treat a crude liquid boron fuel which had been prepared from the reaction of diborane and ethylene at elevated temperatures and superatmospheric pressure. The results of some of these tests are shown in Table II.

Table II Solid Cone. of Vol. Ratio Components CHaOH, Mixture In Product Wt. percent to Fuel Fuel, wt.

percent In order to compare the effect on the fuel of the treatment wherein an alcohol is used with that of the process in which a hydrocarbon alone is the treating material, several crude liquid boron fuels were treated by both methods and the analyses and recoveries were compared. In the alcohol method, a 2% mixture and 30:1 volume ratio were used; the results are shown below in Table III.

As these results indicate, both the boron content of the liquid boron fuels produced from the methanol-pentane treatment and the recovery of the fuel are at least comparable to the results obtained from the use of pentane alone.

Still other tests have shown that the boron fuels are not adversely affected by contact with mixtures of alcohol and hydrocarbon for periods of at least six days. It has also been found that, while heat is evolved during the treatment, the amount of heat produced is moderate and it can be easily dissipated during treatment. In this connection, it may be noted that volatile by-products and impurities in the crude liquid boron fuel, e.g., unreacted alkyl diboranes, result in increased evolution of heat and gassing, so that it is preferred to remove such volatile components prior to the treatment. This can be accomplished by simple stripping or similar techniques.

The improved liquid boron fuels produced in accordance with this invention may be used for the same purposes and in the same manner as the crude liquid boron fuel treated. Thus, in a broad sense, these fuels can be simply burned to provide heat. However, they are also useful as high energy fuels in rocket engines or engines of similar design, wherein they may be combusted with conventional oxidizers, such as liquid oxygen, to produce more thrust than is obtained when hydrocarbon fuels are used in a similar manner.

According to the provisions of the patent statutes, I have explained the principle and mode of practicing my invention, and have described What I now consider to be its best embodiments. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Iclaim:

1. A method of producing an improved liquid boron fuel which comprises contacting a crude liquid boron fuel produced from a boron hydride and an unsaturated hydrocarbon with a mixture of a fluid saturated hydrocarbon in liquid form and a liquid alcohol in an amount suflicient to form two liquid layers, and recovering the improved liquid boron fuel which comprises the top layer.

2. A method in accordance with claim 1 in which the concentration of alcohol in the said mixture is between about 2% and by weight.

3. A method in accordance with claim 1 in which the alcohol is methanol.

4. A method in accordance with claim 1 in which the volume ratio of the said mixture to said crude liquid boron fuel is at least about 10 to 1.

5. A method of producing an improved liquid boron fuel which comprises contacting a crude liquid boron fuel produced from diborane and ethylene under pressure with a mixtureof pentane and methanol in which the concentration of the methanol is between aboupt 2% and 10% by weight whereby two liquid layers are formed, and recovering the improved liquid boron fuel which comprises the top layer.

6. A method in accordance with claim 5 in which the volume ratio of said mixture to said crude liquid boron fuel is at least about 10 to 1.

7. A method in accordance with claim 5 in which the concentration of methanol is between about 3% and 6% by Weight and the volume ratio of said mixture to said crude liquid boron fuel is about to 1.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE, OF CORRECTIGN Patent No, 3.067 .257 December 4, 1962 Timothy Altares Jr,

It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below Column 3, line 67 for "of", second occurrence, read to column 5, line 17 after "alcohol" insert selected from the group consisting of liquid alkanols and benzyl alcohol --a Signed and sealed this 25th day of June 1963,

(SEAL) Attest:

DAVID L. LADD Commissioner of Patents ERNEST W. SWIDER Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,067,257 December 4, 1962 Timothy Altares, Jr 7 It is hereby certified that error appears in the above numbered pat- ,ent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 67, for "of", second occurrence, read to column 5, line 17, after "alcohol" insert selected from the group consisting of liquid alkanols and benzyl alcohol Signed and sealed this 25th day of June 1963,,

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents 

1. A METHOD OF PRODUCING AN IMPROVED LIQUID BORON FUEL WHICH COMPRISES CONTACTING A CURDE LIQUID BORON FUEL PRODUCED FROM A BORON HYDRIDE AND AN UNSATURATED HYDROCARBON WITH A MIXTURE OF A FLUID SATURATED HYDROCARBON IN LIQUID FORM A LIQUID ALCOHOL IN AN AMOUNT SUFFICIENT TO FORM TWO LIQUID LAYERS, AND RECOVERING THE IMPROVED LIQUID BORON FUEL WHICH COMPRISES THE TOP LAYER. 